From 9152d8da37f7b0603f1a5c63210bf4f208fe3f91 Mon Sep 17 00:00:00 2001
From: Scott Sanderson <scoutoss@gmail.com>
Date: Mon, 29 Sep 2014 10:52:53 -0400
Subject: [PATCH] DOC: Slightly better comment on Frequency._ffill.

---
 zipline/history/history.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/zipline/history/history.py b/zipline/history/history.py
index 21b726a3..027ffe45 100644
--- a/zipline/history/history.py
+++ b/zipline/history/history.py
@@ -258,7 +258,8 @@ class HistorySpec(object):
         self.frequency = frequency
         # The field, e.g. 'price', 'volume', etc.
         self.field = field
-        # Whether or not to forward fill the nan data.
+        # Whether or not to forward fill nan data.  Only has an effect if this
+        # spec's field is in FORWARD_FILLABLE.
         self._ffill = ffill
 
         # Calculate the cache key string once.